Such devices are well known and find many applications, notably in the field of portable telephones that use a great many frequency channels determined by the synthesizer. It will be recollected that a synthesizer is formed, in essence, by a voltage-controlled variable oscillator slaved to a reference frequency after a frequency division that ultimately determines the output frequency of the synthesizer.
When the device is in the stand-by mode, it is more or less periodically to be connected to the network and, for reasons of saving energy, it is desirable for the synthesizer to be longest possible in the state of rest, that is, that this implies that the variable oscillator is synchronized with the reference frequency in the fastest possible way. One of the elements that enable to obtain a fast synchronization is the phase discriminator. In patent document EP 0 500 014 the description of such a discriminator can be found.
If this known discriminator offers good indications as regards the phase differences between -.pi. and +.pi., these indications are no longer sufficient for greater phase differences, thus for signals having different frequencies.